The present invention relates to a thin, flexible film made of a transparent material having a structured surface on one side and a smooth surface opposite the structured surface on the other side, one aspect of which is that the combination of surfaces may totally internally reflect light.
It is well known, to those skilled in the art, to form thin, flexible films structured on one side to deflect light, as illustrated in U.S. Pat. No. 2,248,638. In addition, mirrors have been used to reflect light and the making of mirrors is also well known to those skilled in the art as described in, for example, U.S. Pat. No. 2,723,919. However, there are limitations associated with the use of mirrors. Commercially available mirrors, even when new, have limited reflectivities that normally range from about 75% to about 95%, and, when, with the passing of time, the reflective coating becomes tarnished, the efficiency decreases.
The principle of total internal reflection has been recognized by optical engineers, as an alternative to mirrors, for many decades for reflectors and luminairs, as illustrated in U.S. Pat. Nos. 2,175,067 and 4,260,220. Its application can be found in various optical instruments, for example, the porro prisms in certain binoculars, the amici roof prisms used in certain types of periscopes, and the roof prisms used in certain types of single lens reflex cameras. However, such devices are massive and bulky.
The present invention affords an improved thin, flexible film made of a transparent material having a structured surface on one side which will achieve total internal reflection so that light, incident within certain angular ranges, is totally internally reflected. In addition, since the improved film requires no coating, it is capable of maintaining its efficiency over long periods of time. Finally, because of the film's flexibility, it can be formed into a variety of shapes and utilized in several ways.